Alternate BaseURLs not used for init segments

[bbert]

Environment

• The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page

• Link to playable MPD file:
  https://www.content-steering.com/bbb/playlist_steering_cloudfront_https.mpd
• Dash.js version:
  nightly
• Browser name/version:
• OS name/version:

Steps to reproduce

1. Please provide clear steps to reproduce your problem

• Open content steering demo page: https://reference.dashif.org/dash.js/nightly/samples/advanced/content-steering.html
• Using devtools you can block the request corresponding to the 1st init segment that will be requested
• Launch the stream

2. If the bug is intermittent, give a rough frequency if possible

Observed behavior

Once all retry attempts have been done for init segment, the player will stop requesting without trying alternate BaseURLs

Console output

Paste the contents of the browser console here.
You may need to enable debug logging in dash.js by calling player.updateSettings({ 'debug': { 'logLevel': dashjs.Debug.LOG_LEVEL_DEBUG }}) if you are using your own page.

Expected behavior

The player should try loading the init segment using the next available alternate BaseURL

[dsilhavy]

Fixed in #4533, thanks @bbert